It is well established practice to employ a grid when making radiographs (X-ray pictures) of various portions of a patient's body when the part to be examined is greater than 10cm. In the case of a radiographic table, there is normally provided a carriage which supports a film cassette arranged to move beneath a cover transparent to the X-rays. The film can thus be positioned under different portions of the patient's body while lying on the cover. The grid itself is also carried on the carriage immediately above the film and beneath the patient.
The function of the grid is to absorb scattered radiation passing through the patient's body to the film. The grid itself in this respect includes multiple parallel strips of lead or X-ray absorbing material held in specific spaced relationship by wood or plastic strips.
With the foregoing arrangement, it is found that superior radiographs can be obtained. On the other hand, faint parallel lines will show up on the developed picture resulting from the presence of the grid. To overcome this latter difficulty, it is common practice to move the grid in a direction transverse to the direction of the strips during exposure, this motion being just sufficient to avoid "photographing" the grid itself along with the desired image.
While vast improvements have been made in radiographic tables and grid structures, there has been little if any advance in the means provides for moving the grid during exposure. Generally, such systems as are used are mechanical in nature will simply oscillate the grid back and forth. There are two major problems with such arrangements. First, the mechanical vibrating or moving of the grid is noisy to the extent that it can alarm the patient possibly resulting in the patient himself moving during exposure, thus resulting in a blurred image. Second, the mechanics involved to move the grid can result in vibrations of the table itself, or carriage supporting the grid and film also resulting in blurring. This latter problem has become more pronounced when shorter exposures require faster grid movement.